Heat exchanger reinforcing means



June 11, 1968 w. DROBKA HEAT EXCHANGER REINFORCING MEANS 5 Sheets-Sheet 1 Filed July 6. 1966 Inventor.-

June 11, 1968 w. DROBKA 3,387,652

HEAT EXCHANGER REINFORCING MEANS Filed July 6. 1966 5 Sheets-Sheet 2 Inven tor.-

June 11, 1968 w. DROBKA 3,387,652

HEAT EXCHANGER REINFORCING MEANS Filed July 6, 1966 3 Sheets-Sheet 5 United States Patent 3,387,652 HEAT EXCHANGER REINFORCING MEANS Witold Drobka, Berlin, Germany, assiguor to Borsig Aktiengesellschaft, Berlin, Germany Filed July 6, 1966, Ser. No. 563,288 5 Claims. (Cl. 165162) ABSTRACT OF THE DISCLOSURE A heat exchanger with a thin bottom wall which is reinforced by two. groups of plate means arranged on edge and anchored to the bottom for reinforcing the latter while being supported by the lower portion of the tubular member forming the outer mantle of the heat exchanger while one group of said plate means extends in a direction transverse to the plate means of the other group, and while the lower edge of said plate means is spaced from said bottom so as to define therewith a chamber communicating with inlet means passing through said mantle.

The present invention relates to a pipe assembly with a relieved thin pipe bottom facing the hot substance for a heat exchange between substances of high pressure difference at high temperatures.

Frequently, the problem arises to transfer the sensible heat contained in hot substances of low pressure indirectly as far as possible to substances the medium temperature of which in the heat exchanger is relatively low while the pressure of said last mentioned substances is relatively high. As a typical example for instances referred to above, there may be mentioned the so-called waste heat boilers for exploiting the waste gases contained in flue or process gases. These gases frequently contain impurifications which in the course of time cause soiling of the heat transfer surfaces and increasingly reduce the heat transfer.

In view of the high pressure drop and the necessity of affording a possibility to clean all surfaces subject to the formation of crusts, it is customary to employ a pipe assembly through which hot gases are passed. With arrangements of this type, there exists the danger that at the outlined conditions of operation a local overheating occurs with the result that the strength of the parts is affected particularly of structural elements which are under high load as for instance the pipe bottom at the entrance of the pipes.

The pipe bottom forms a plane wall with uniformly distributed bores for the passage of the hot substances. The flow velocity of the hot substances relative to the plane end face of the bottom varies from zero at the damming up or collecting points between the bores to a maximum value at the centers of the bores. When disregarding these local differences in the interest of a clearer examination of the qualitative connections, the bottom may approximately be considered a plane wall which transfers an hourly quantity of heat Q through the surface F from the hotter medium to the colder medium. The maximum wall temperature at the surface contacted by the warmer substance is t '=t Q/a F=t q/a In this equation, t represents the temperature of the warmer medium at a greater distance from the wall, whereas 01 represents the heat transfer number from the warmer substance to the wall, and q represents the heat flow density.

correspondingly, the low wall temperature while t represents the temperature of the colder substance with increasing distance from the wall, whereas a represents the heat transfer number between the wall 3,387,652 Patented June 11, 1968 "ice and the colder substance. Furthermore, in conformity with the basic equation of the heat transfer In this equation, k represents the heat exchange number, and At represents the tmeperature difference (t t Consequently, t =t At k/ 11 and In view of the relationship k=1/(1/ x +6/)\+1/a with A indicating the thickness of the wall and indicating the heat conducting number of the material of the wall, there is obtained the following equation:

and

A particularly low wall temperature may therefore be expected in the above mentioned waste heat boilers in which the heat transfer number a from the hot gas of low pressure to the wall is relatively low and the heat transfer number a from the wall to the flowing or evaporating liquid is relatively high. An optimum can thus obviously be obtained when with a given wall material and thus with a given A, in conformity with the invention, the wall thickness A is reduced to a technically admissible minimum. Such an arrangement is particularly effective in connection with waste heat boilers because the value appearing in the parentheses of the last mentioned equation for the heat transfer resistance 1/ a is low with regard to the heat resistance 6/)\.

In order to avoid the above outlined drawbacks, and

on the basis of the above mentioned thermodynamic consideration, according to the present invention, the pipe bottom facing the hot substance is relieved from the forces created by the pressure drop between the media contacting said bottom. This is effected by devices which for purposes of maintaining the strength of material prevailing at normal temperature, are arranged in the sphere of influence of the colder substance. Consequently, the said pipe bottom may in an extreme instance, for obtaining as low temperatures as possible at the end face facing the hot flow of substances, be made so thin as the close connection of the pipes in the pipe bottom will technically permit.

According to a further development of the present invention, the relief of the pipe bottom is effected through the intervention of anchors by a net-shaped supporting bottom which is surrounded by the colder substance While the pipes are passed through the meshes of said netshaped supporting bottom.

The invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIGS. 1 to 3 represent a waste boiler, and in which, more specifically FIG. 1 is a longitudinal section along the line 1-1 of FIG. 2.

FIG. 2 is a cross section taken along the line II-II of FIG. 1.

FIG. 3 is a longitudinal section along the line III-III of FIG. 2.

As will be seen from the drawings, the outer wall 1 is at each end provided with flanges 2 which cooperate with counter flanges 3 which are connected to each other by bolts 4 and between which are arranged seals or gaskets 5. The hot substance passes from the bottom through the upwardly flaring and only partially illustrated entrance connection 6 to the thin pipe bottom 7 where it is distributed over and through pipes 8. Pipes 8 have their upper cold end closely connected to the normal top portion 9 and lead into the upwardly tapering and only partially illustrated discharge connection 10. The colder substance, according to the embodiment shown enters through the connection 11 and passes into an annular chamber 12 from where it flows through the radial passages 13 into deviating passages 14 which distribute the said colder substance substantially uniformly and convey it to the pipe bottom 7. The said colder substance will within the chamber 15 absorb heat from the hotter substance through the wall of the pipes 8 j and will leave the device through the connection 16. The pipe bottom 7 is in conformity with the present invention designed as thin as a close connection of the pipes 8 in bottom 7 will technically permit. However, also greater wall thicknesses for the pipe bottom 7 are according to the invention not excluded. Between the pipes 8, there are connected to the bottoms 7, for instance by welding, anchors 17 which are connected to supporting plates 18 arranged on edge. These supporting plates 18, according to the specific embodiment shown in the drawings, rest on the supporting members 19 which in their turn rest on an inner extension of the outer wall 1. Ribs 20 reinforce the relatively thin supporting plates 18 against bulging, while the guiding plates 21 form guiding passages 14. It is to be understood that the present invention is not limited to the particular arrangement referred to above of the supporting elements 17 to 20 of the pipe bottom 7. Any other construction whose supporting parts for maintaining the strength properties within the range of the cold substance are so arranged that the guiding of pipes 8 will not be impeded, may be employed within the framework of the present invention. When the colder medium is liquid and in the outer wall space 15 will be subjected to evaporation in a condition of saturation, the annular passage 12 and the guiding plates 21 for forming the guiding passages 14 may be omitted. In this instance, a single radial passage 13 along the axis of the entrance connection 11 for introducing the colder substance will suffice.

It is, of course, to be understood that the present invention is, by no means, limited to the particular arrangement shown in the drawings but also comprises any modifications within the scope of the appended claims.

What I claim is:

1. A heat exchanger which includes: a tubular memher having a tubular wall with a bottom connectable to means conveying a iiow of hot gas and also having a top adapted to be connected to a discharge, a plurality of pipes arranged within said tubular member is radially spaced relationship to each other and to the inside of said tubular wall, said pipes having their ends respectively connected to said top and bottom so as to establish communication between the outside of said bottom and the outside of said top whereby a flow of hot gas can pass from the outside of and through said bottom through said pipes and said top to the outside thereof, said bottom being relatively thin with regard to the top and having a thickness just sufficient to assure a gas-tight connection of the respective adjacent pipe ends to said bottom, two groups of plate means supported by the lower portion of said tubular member and arranged on edge with the lower edges of said plate means spaced from said bottom so as to define therebetween a chamber for receiving the medium to be heated, the upper edges of said plate means being spaced from said top while extending upwardly substantially parallel to the axis of said tubular member, anchoring means anchoring said plate means to said bottom for reinforcing the latter, the plates of one group extending in a direction transverse to the plates of the other group so as to define compartments with each other, said pipes extending through said compartments, and inlet means extending through said tubular wall for feeding the substance to be heated up into said chamber.

2. A heat exchanger according to claim 1, which includes annular passage means leading from said inlet means to said chamber for deviating and directing the substance to be heated into said chamber.

3. A heat exchanger according to claim 1, in which said plates extend upwardly over a portion only of the height of said tubular member.

4. A heat exchanger according to claim 1, in which said plates extend upwardly to a level slightly above said inlet means.

5. A heat exchanger according to claim 1, in which said plates extend upwardly over a portion only of the height of said tubular member just sutficient to prevent warping of said bottom in view of the temperature drop between the outside and the inside of said bottom.

References Cited UNITED STATES PATENTS 1,489,932 4/1924 Dickey 16S161 1,809,915 6/1931 Smith 82 XR 3,055,641 9/1962 Miller 165161 XR 3,301,321 1/1967 Poore 16S-82 XR ROBERT A. OLEARY, Primary Examiner.

M. A. ANTONAKAS, Assistant Examiner. 

